I helped some community users on IRC recently which run into issues when migrating to 4.0, and the most popular issue I'm seeing is caused by the hibernate-anntations module dependency, so, I would like to explain it again.

we MERGED this module into hibernate-core since hibernate core 3.6 release, see the release note of 3.6.

so, maven / gradle users, you just need to add hibernate-core ( and hibernate-entitymanager if you're using JPA ) to your dependency list, and remove hibernate-annotation dependency if it is there.

some background:

before hibernate-core 3.5, it was JDK 1.4 compatible, so, to use Annotation, the new feature of JDK 1.5, we had to create a new module, aka, hibernate-annotations

but since we had moved to JDK 1.5 since hibernate-core 3.5, there is no reason to keep hibernate-annotations as a separated module, so, we merged back into hibernate-core.